Add support for round(T, x) where T <: Integer (and friends)

src/Unitful.jl

@@ -870,11 +870,16 @@ end
 ==(x::Number, y::Quantity) = ==(y,x)
 <=(x::Quantity, y::Quantity) = <(x,y) || x==y
 
-for f in (:floor, :ceil, :trunc, :round, :isinteger)
-    @eval ($f)(x::Quantity) = error("$($f) can only be well-defined for dimensionless ",
+_dimerr(f) = error("$f can only be well-defined for dimensionless ",
         "numbers. For dimensionful numbers, different input units yield physically ",
         "different results.")
+isinteger(x::Quantity) = _dimerr(isinteger)
+isinteger(x::DimensionlessQuantity) = isinteger(uconvert(NoUnits, x))
+for f in (:floor, :ceil, :trunc, :round)
+    @eval ($f)(x::Quantity) = _dimerr(f)
     @eval ($f)(x::DimensionlessQuantity) = ($f)(uconvert(NoUnits, x))
+    @eval ($f){T<:Integer}(::Type{T}, x::Quantity) = _dimerr(f)
+    @eval ($f){T<:Integer}(::Type{T}, x::DimensionlessQuantity) = ($f)(T, uconvert(NoUnits, x))
 end
 
 zero(x::Quantity) = Quantity(zero(x.val), unit(x))

test/runtests.jl

@@ -776,10 +776,26 @@ end
     @test_throws ErrorException ceil(3.7m)
     @test_throws ErrorException trunc(3.7m)
     @test_throws ErrorException round(3.7m)
+    @test_throws ErrorException floor(Integer, 3.7m)
+    @test_throws ErrorException ceil(Integer, 3.7m)
+    @test_throws ErrorException trunc(Integer, 3.7m)
+    @test_throws ErrorException round(Integer, 3.7m)
+    @test_throws ErrorException floor(Int, 3.7m)
+    @test_throws ErrorException ceil(Int, 3.7m)
+    @test_throws ErrorException trunc(Int, 3.7m)
+    @test_throws ErrorException round(Int, 3.7m)
     @test floor(1.0314m/mm) === 1031.0
     @test ceil(1.0314m/mm) === 1032.0
     @test trunc(-1.0314m/mm) === -1031.0
     @test round(1.0314m/mm) === 1031.0
+    @test floor(Integer, 1.0314m/mm) === Integer(1031.0)
+    @test ceil(Integer, 1.0314m/mm) === Integer(1032.0)
+    @test trunc(Integer, -1.0314m/mm) === Integer(-1031.0)
+    @test round(Integer, 1.0314m/mm) === Integer(1031.0)
+    @test floor(Int16, 1.0314m/mm) === Int16(1031.0)
+    @test ceil(Int16, 1.0314m/mm) === Int16(1032.0)
+    @test trunc(Int16, -1.0314m/mm) === Int16(-1031.0)
+    @test round(Int16, 1.0314m/mm) === Int16(1031.0)
 end
 
 @testset "Sgn, abs, &c." begin